It is well known that if two surfaces of insulating materials are rubbed together and then separated, an electrostatic charge will build up between the two surfaces. In recent years, this problem in computer room flooring and desk areas has been troublesome, since the discharge of built-up static can result in tape or disc erasures and interference with sensitive equipment. Such charged surfaces in hospital surgical, and other areas where certain anesthetic gases can form violently explosive mixtures with air, has caused even greater concern that the chances of explosions caused by sparks or electrical discharges be minimized. In all of these cases, the static build-up can be caused by walking on flooring, moving electronic components or other equipment from place to place, and even utilizing the keyboard on a computer terminal. Such static build-up can also occur over a period of time in the wearing apparel of workers.
Charlton et al., in U.S. Pat. No. 3,040,210 recognized these problems, and taught resilient, decorative, carbon containing, linoleum floor sheeting, laminated to a conductive base. The linoleum surface sheeting contains from 1 percent to 14 weight percent conductive carbon, homogeneously mixed with other conductive materials, binder, and sufficient coloring pigments to provide an attractive appearance. The conductive backing must contain from 10 percent to 35 weight percent conductive carbon, and can be bonded to fabric for added strength, where the fabric itself can be made conductive by initially dipping it in a dispersion of conductive carbon. This provides a static resistant flooring having a controlled electrical resistance, which will wear evenly, can be applied in long sections minimizing seams, and which is resilient enough to help reduce fatigue for people that must stand or walk on the flooring for long periods of time.
Eastes, in U.S. Pat. No. 3,515,580, taught antistatic coating solutions or emulsions that can be used on polymeric surfaces, such as films, tubing and other solid structures. These surface coating solutions or emulsions contain a mixture of urea; a selected metal salt, such as lithium chloride, lithium nitrate, zinc chloride, zinc acetate, magnesium bromide, magnesium nitrate, and aluminum hydroxy diacetate, among many others, and preferably, sodium nitrate, sodium acetate or potassium acetate; wetting agent, such as an alkyl diester of sulfosuccinic acid; and a carrier, such as water. p Berbeco, in U.S. Pat. No. 4,301,040, taught static-free mats containing a standard, non-conductive decorative laminate, such as a 0.16 cm. (1/16 in.) thick melamine-formaldehyde laminate, or a rubber, nylon, polycarbonate, polyethylene or polypropylene, non-conductive sheet, as a top surface, adhesive bonded to, or coated with, either an electrically conductive solid or an open cell foam bottom backing layer. The bottom layer includes a polymeric material or a foam and an antistatic amount, generally about 2 percent to 40 weight percent, of conductive particulate material, such as metal particles, aluminum salts such as aluminum silicate, graphite fibers, and preferably carbon black particles. Useful polymeric materials include butadiene-styrene resin and the like, and useful foams include polyurethane foams, polyester foams and the like. When a foam is used as the bottom layer, a flexible cushion mat results.
Standard decorative laminates are non-conductive through their cross-section, and are described, for example, by McCaskey, Jr. et al., in U.S. Pat. No. 4,061,823. They are popular as surfacing material for counter and furniture tops. Because, in many cases, they must be machined, fillers other than coloring pigments are usually avoided. Such laminates generally contain 2 to 6 fibrous, Kraft paper sheets, impregnated with phenol-aldehyde resin, as a core for 1 high quality, fibrous, alpha-cellulose decorative print sheet, having a pattern or plain color, impregnated with melamine-aldehyde resin, and 1 top, high quality, fibrous, alpha-cellulose overlay protective sheet, also impregnated with melamine-aldehyde resin. Any pigmentation fillers would only be present in the decorative print sheet.
The Charlton et al. material requires use of large amounts of relatively expensive carbon, and requires a complicated manufacturing process. The Eastes surface coating would be prone to wear off any surface subject to hard use, and the Berbeco material requires a non-conductive surface, through which the backing would have to draw static charges. Of course, standard decorative laminates are usually non-conductive. What is needed is a surfacing material having oustanding antistatic properties, good wear properties, and an attractive appearance, and which is also inexpensive, easy to manufacture, and thin enough to allow ease of installation.